The present invention relates to novel flame-retardant resin compositions.
Thermoplastic resins are used as materials for producing various devices in many fields such as office automation devices, household electrical appliances, etc. because of their excellent molding processability, mechanical properties, appearance and like features. These resins are often required to have flame retardancy depending on use to eliminate problems on exposure to heat and ignition.
In order to impart flame retardancy to thermoplastic resins, it is general to add a halogen-containing organic compound as a flame retardant, such as tetrabromobisphenol A, decabromodiphenyl oxide or the like. However, the inclusion of halogen-containing organic compounds poses problems of reducing the thermal stability of a thermoplastic resin as the matrix, corroding the mold with a gas given off on decomposition of halogen-containing organic compound during molding, or producing as by-product low molecular toxic halogen compounds in molding or on combustion.
Halogen-free phosphoric ester compounds have been proposed as flame retardant for thermoplastic resins. Compositions are proposed in which triphenylphosphate/polytetrafluoroethylene (PTFE) or condensable phosphoric ester/PTFE are incorporated in a resin mixture of aromatic polycarbonate and rubber-fortified styrene resin (European Patent No. 174,493 and Dutch Patent No. 8,802,346), in which a crystalline powdery aromatic diphosphate compound is added to a thermoplastic resin (Japanese Unexamined Patent Publication No. 1079/1993 and U.S. Pat. No. 5,122,556), etc. Halogen-free phosphoric ester compounds have the drawback of adversely affecting the mechanical properties and molding processability of thermoplastic resins although capable of imparting a certain degree of flame retardancy to thermoplastic resins. Further, phosphoric ester compounds tend to plasticize a resin and thus are likely to cause dripping (falling of live charcoal during burning), so that a dripping inhibitor such as PTFE is essentially used. Especially the prevention of dripping is required for attaining a V-0 level of flame retardancy in a test according to the flame retardancy test UL-94 (Test for Flammability of Plastic Materials for Parts in Devices and Appliances UL-94, Fourth Edition).
On the other hand, in order to impart flame retardancy to a resin composition comprising a thermotropic liquid crystal polymer and other thermoplastic resin, use is made of a bromine-containing organic compound such as brominated polystyrene (Japanese Unexamined Patent Publication No. 179051/1991), a phosphoric ester compound (Japanese Unexamined Patent Publications No. 331051/1995 and No. 59524/1997) or the like. However, the incorporation of a bromine-containing organic compound results in lower thermal stability, corrosion of mold during molding process and generation of toxic bromine compounds, as in the above-mentioned case. When a phosphoric ester is used, it is essential to jointly add a dripping inhibitor such as PTFE, a fibrous inorganic filler or the like.
An object of the present invention is to provide a novel flame-retardant resin composition which is free of the foregoing-problems of the prior art.
Another object of the invention is to provide a novel flame-retardant resin composition which is free of the problems arising due to the presence of halogen element, excellent in flame retardancy, mechanical properties, molding processability and the like, and unlikely to cause dripping without use of a dripping inhibitor.
Other objects and features of the invention will become apparent from the following description.
The present inventors carried out extensive research to overcome the foregoing problems and found that when a specific flame retardant is added to a mixture of a thermotropic liquid crystal polymer and other thermoplastic resin, the obtained flame-retardant resin composition is excellent in flame retardancy, mechanical strength, and molding processability, and eliminates the need for a dripping inhibitor. The present invention was completed based on this novel finding.
According to the present invention, there is provided a flame-retardant resin composition comprising:
(A) 100 parts by weight of a thermoplastic resin other than a thermotropic liquid crystal polymer,
(B) 0.01 to 50 parts by weight of a thermotropic liquid crystal polymer, and
(C) 1 to 30 parts by weight of a halogen-free phosphazene compound.
The flame-retardant resin composition of the present invention contains, as essential components, (A) a thermoplastic resin other than a thermotropic liquid crystal polymer, (B) a thermotropic liquid crystal polymer, and (C) a halogen-free phosphazene compound.
Conventional resins may be used as the thermoplastic resin (A) other than a thermotropic liquid crystal polymer in the composition of the invention. Examples of such resins are polyethylene, polypropylene, polyisoprene, polybutadiene, polystyrene, high impact-resistant polystyrene (HIPS), acrylonitrile-styrene resin (AS resin), acrylonitrile-butadiene-styrene resin (ABS resin), methyl methacrylate-butadiene-styrene resin (MBS resin), methyl methacrylate-acrylonitrile-butadiene-styrene resin (MABS resin), acrylonitrile-acrylic rubber-styrene resin (AAS resin), polyalkyl (meth)acrylate, aromatic polycarbonate (PC), polyphenylene ether (PPE), polyphenylene sulfide (PPS), polyether sulfone (PES), polysulfone (PSU), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyamide (PA), polyether ketone (PEK), polyether ether ketone (PEEK), polyamide imide (PAI), polyether imide (PEI), Aft polyimide (PI), etc. Among them, preferred are PC, PBT, PPE, ABS resins, HIPS and the like. These resins may be used either alone or in combination. Preferred combinations of two of the resins are PC/ABS, PC/PBT, PPE/HIPS and the like. Among them, PC/ABS is more preferable. The ratio (by weight) of two resins in this case is usually 10-90/90-10, preferably 20-80/80-20.
The thermotropic liquid crystal polymer (B) in the composition of the invention is not known to have drip inhibitory activity itself, but is considered to act as a dripping inhibitor in coexistence with a halogen-free phosphazene compound as in the composition of the invention. Stated more specifically, the thermotropic liquid crystal polymer densely and firmly reinforces the thermoplastic resin so as not to form an inflammable low molecular compound within the thermoplastic resin during combustion, thereby preventing the resin from becoming less viscous with the result that the resin can be inhibited from inducing the level of dripping specified in the flame retardancy test (UL-94) in the presence of the phosphazene compound.
As the thermotropic liquid crystal polymer (B), known polyester-based polymers can be suitably used. Examples are main-chain type liquid crystal polymers such as those having, as main structural units, aromatic hydroxycarboxylic acid, polyalkylenediol and aromatic dicarboxylic acid; those having, as main structural units, aromatic hydroxycarboxylic acid and hydroxynaphthoic acid; and those having, as main structural units, aromatic hydroxycarboxylic acid, aromatic dicarboxylic acid and dihydroxybiphenyl; and side chain-type liquid crystal polymers such as those having polyphosphazene as a main chain and polyalkylenediol and aromatic carboxylic acid as side chains; and those having polyphosphazene as a main chain and poly(alkyleneoxy)alkoxyazobenzene as a side chain. Among them, preferred are polymers having p-hydroxybenzoic acid and polyethylene terephthalate as main structural units, those having p-hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid as main structural units, and a polycondensate of said polymer with a dihydroxy compound and/or dicarboxy compound. The flame retardancy (especially a degree of drip inhibition) and mechanical properties can be further improved by using suitably selected dihydroxy compounds and dicarboxy compounds. Useful dihydroxy compounds are, for example, ethylene glycol, hydroquinone, 2,6-dihydroxynaphthalene, 4,4xe2x80x2-dihydroxybiphenyl, bisphenol A and the like. Among them, preferred are ethylene glycol, hydroquinone, 4,4xe2x80x2-dihydroxybiphenyl and the like, and more preferred are ethylene glycol, hydroquinone and the like. Examples of dicarboxy compounds are terephthalic acid, isophthalic acid, 2,6-dicarboxynaphthalene and the like. Among them, terephthalic acid and isophthalic acid are preferable, and terephthalic acid is more preferable. The dihydroxy compounds and dicarboxy compounds can be used either alone or in combination. When terephthalic acid is used as the dicarboxy compound, the amount of the terephthalic acid used is at least 40% by weight, preferably at least 60% by weight, based on the total amount of dihydroxy compound and/or dicarboxy compound. The flame-retardant resin composition can be further improved in flame retardancy, mechanical strength and the like by using at least 40% by weight of terephthalic acid.
The amount of the thermotropic liquid crystal polymer (B) used is usually 0.01 to 50 parts by weight, preferably 0.1 to 40 parts by weight, more preferably 0.5 to 30 parts by weight, per 100 parts by weight of the thermoplastic resin (A) other than said polymer, in view of the mechanical properties (especially toughness), flame retardancy, fluidity and other properties of the obtained flame-retardant resin composition.
The halogen-free phosphazene compound (C) in the composition of the invention (hereinafter referred to as xe2x80x9chalogen-free phosphazene compoundxe2x80x9d) includes known compounds disclosed in patent publications, literature, etc., specifically in James E. Mark, Harry R. Allcock and Robert West, xe2x80x9cInorganic Polymersxe2x80x9d Prentice-Hall International, Inc., 1992, pp. 61-140.
Stated more specifically, the following compounds (1) to (4) can be exemplified.
(1) Cyclic Phosphazene Compounds Represented by the Formula (1) 
wherein m is an integer of 3 to 25, two R1 groups are the same or different and each represents a phenyl group substituted with at least one group selected from the class consisting of alkyl groups having 1 to 6 carbon atoms and an allyl group or an unsubstituted phenyl group.
(2) Straight-chain Phosphazene Compounds Represented by the Formula (2) 
wherein n is an integer of 3 to 1000, R1 is as defined above, X represents a group xe2x80x94Nxe2x95x90P(OR1)3 or a group xe2x80x94Nxe2x95x90P(O)OR1, and Y represents a group xe2x80x94P(OR1)4 or a group xe2x80x94P(O)(OR1 )2.
(3) Crosslinked Phosphazene Compounds Wherein at Least One of the Foregoing Phosphazene Compounds (1) and (2) is Crosslinked with at Least One Crosslinking Group selected from the Class Consisting of o-phenylene Group, m-phenylene Group, p-phenylene Group, Biphenylene Group, and a Group Represented by the Formula 
wherein A is a group xe2x80x94SO2xe2x80x94, a group xe2x80x94Sxe2x80x94, a group xe2x80x94Oxe2x80x94 or a group xe2x80x94C(CH3)2xe2x80x94, each of said crosslinking groups being interposed between the two oxygen atoms left after the elimination of group R1 from the phosphazene compound (1) or (2), and the number of the R1 groups in the crosslinked phosphazene compound being 50 to 99.9% based on the total number of R1 groups in said phosphazene compound prior to the crosslinking.
(4) At Least One Phosphazene Compound Selected from the Group Consisting of Cyclic Phosphazene Compounds Represented by the Formula (3) 
wherein R2 is a cyano-substituted phenyl group; R3 is an alkyl group having 1 to 18 carbon atoms or an aryl group having 6 to 10 carbon atoms; these groups may be substituted with at least one group selected from alkyl groups having 1 to 10 carbon atoms, allyl group and aryl groups; when two or more R3 groups exist, the R3 groups may be the same or different; p and q are numbers which fulfil the requirements that p greater than 0, q. 0, and p+q=2; and r is an integer of 3 to 25, and a straight-chain phosphazene compound represented by the formula (4) 
wherein R2, R3, p and q are as defined above; s is an integer of 3 to 1000; Xxe2x80x2 is a group xe2x80x94P(OR )41 a group xe2x80x94P(OR2)3(OR3), a group xe2x80x94P(OR2)2(OR3)2, a group xe2x80x94P(OR2)(OR3)3, a group xe2x80x94P(OR3)4, a group xe2x80x94P(O)(OR2)2, a group xe2x80x94P(O)(OR2)(OR3), or a group xe2x80x94P(O)(OR3)2; and Yxe2x80x2 is a group xe2x80x94Nxe2x95x90P(OR2)3, a group xe2x80x94Nxe2x95x90P(OR2)2(OR3), a group xe2x80x94Nxe2x95x90P(OR2)(OR3)2, a group xe2x80x94Nxe2x95x90P(OR3)3, a group xe2x80x94Nxe2x95x90P(O)OR2 or a group xe2x80x94Nxe2x95x90P(O)OR3.
The foregoing examples of the halogen-free phosphazene compound (C) can be used either alone or in combination.
Specific examples of the cyclic phosphazene compound (1) and the straight-chain phosphazene compound (2) include a mixture of phosphazene compounds in which phenoxy groups and/or alkoxy groups are introduced as substituents and which are obtainable from a mixture of cyclic and straight-chain chlorophosphazenes, e.g., hexachlorocyclotriphosphazene, octachlorocyclotetra-phosphazene and the like, prepared by reacting ammonium chloride and phosphorus pentachloride at about 120 to about 1 30xc2x0 C.; and hexaphenoxycyclotriphosphazene, octaphenoxycyclotetraphosphazene, decaphenoxycyclo-pentaphosphazene, hexaalkoxycyclotriphosphazene, octaalkoxycyclotetraphosphazene, decaalkoxycyclopenta-phosphazene and like cyclic phosphazene compounds obtained by isolating, from the above mixture of chlorophosphazenes, hexachlorocyclotriphosphazene, octachlorocyclotetraphosphazene, decachlorocyclopenta-phosphazene or like single substances, followed by substitution with a phenoxy group and/or an alkoxy group. Specific examples of the straight-chain phosphazene compound (2) include those obtained by heating (at 220 to 250xc2x0 C.) hexachlorocyclotriphosphazene for ring-opening polymerization to give dichlorophosphazene, followed by substitution with a phenoxy group and/or an alkoxy group.
Specific examples of the crosslinked phosphazene compound (3) are phenoxyphosphazene having 4,4xe2x80x2-sulfonyldiphenylene(bisphenol-S residue) group-crosslinked structure, phenoxyphossphazene having 2,2-(4,4xe2x80x2-diphenylene)isopropylidene group-crosslinked structure, phenoxyphosphazene having 4,4xe2x80x2-oxydiphenylene group-crosslinked structure, phenoxyphoshazene having 4,4xe2x80x2-thiodiphenylene group-crosslinked structure, phenoxyphosphazene having 4,4xe2x80x2-diphenylene group-crosslinked structure, etc.
Specific examples of the phosphazene compounds (4) are monocyanophenoxypentaphenoxycyclotriphosphazene, dicyanophenoxytetraphenoxycyclotriphosphazene, tricyanophenoxytriphenoxycyclotriphosphazene, tetracyanophenoxydiphenoxycyclotriphosphazene, pentacyanophenoxymonophenoxycyclotriphosphazene and like cyclotriphosphazene compounds; monocyanophenoxyhepta-phenoxycyclotetraphosphazene, dicyanophenoxyhexaphenoxycyclotetraphosphazene, tricyanophenoxypentaphenoxy-cyclotetraphosphazene, tetracyanophenoxytetraphenoxy-cyclotetraphosphazene, pentacyanophenoxytriphenoxycyclotetraphosphazene, hexacyanophenoxydiphenoxy-cyclotetraphosphazene, heptacyanophenoxymonophenoxy-cyclotetraphosphazene and like cyclotetraphosphazene compounds; cyclopentaphosphazene compounds having both cyanophenoxy and phenoxy groups as substituents; and like cyclic phosphazene compounds; and straight-chain phosphazene compounds having both cyanophenoxy and phenoxy groups as substituents.
Among these compounds, preferred are a mixture of phenoxyphosphazene compounds which have phenoxy groups as substituents and which are obtainable from a mixture of cyclic and straight-chain chlorophosphazenes, phenoxyphosphazene having 4,4xe2x80x2-sulfonyldiphenylene-crosslinked structure; phenoxyphosphazene having 2,2-(4,4xe2x80x2-diphenylene)-isopropylidene group-crosslinked structure; and phosphazene compounds having both cyanophenoxy and phenoxy groups as substituents.
The halogen-free phosphazene compound (C) used is 1 to 30 parts by weight, preferably 5 to 20 parts by weight, per 100 parts by weight of the thermoplastic resin (A) other than the thermotropic liquid crystal polymer, in view of the mechanical strengths (especially toughness), flame retardancy and other properties of the obtained flame-retardant resin composition.
The essential components in the flame-retardant resin composition of the present invention, i.e.the thermoplastic resin (A), the thermotropic liquid crystal polymer (B) and the halogen-free phosphazene compound (C), can be used in various forms such as powders, beads, flakes, pellets, etc.
The flame-retardant resin composition of the invention may contain conventional additives and fillers for resin within the ranges of amounts which do not adversely affect the desired properties. Examples of useful additives include flame retardants other than the halogen-free phosphazene compounds, UV absorbers, light stabilizers, antioxidants, light screens, metal deactivators, quenching agents, heat resistance stabilizers, lubricants, mold releasing agents, coloring agents, antistatic agents, antiaging agents, plasticizers, impact strength improving agents, compatibilizers and the like. Useful fillers include, for example, mica, kaolin, talc, silica, clay, calcium carbonate, calcium sulfate, calcium silicate, glass beads, glass balloons, glass flakes, glass fibers, fibrous alkali metal salts of titanic acid (potassium titanate fibers, etc.), fibrous transition metal salts of boric acid (aluminum borate fibers, etc.), fibrous alkaline earth metal salts of boric acid (magnesium borate fibers, etc.), zinc oxide whiskers, titanium oxide whiskers, magnesium oxide whiskers, gypsum whiskers, aluminum silicate whiskers, calcium silicate whiskers, silicon carbide whiskers, titanium carbide whiskers, silicon nitride whiskers, titanium nitride whiskers, carbon fibers, alumina fibers, alumina-silica fibers, zirconia fibers, quartz fibers, metal fibers and the like. These additives and fillers can be used either alone or in combination.
The flame-retardant resin composition of the invention can be prepared from the thermoplastic resin (A), the thermotropic liquid crystal polymer (B) and the halogen-free phosphazene compound (C) in specified amounts, optionally in combination with additives and fillers, by mixing and/or kneading the components by conventional methods. The components may be fed all at one time, or two or three components may be mixed, and remaining components may be added and mixed in a suitable order. For example, the mixture of components may be mixed and/or kneaded using an extruder such as a single screw extruder or a twin-screw extruder, or a kneader such as Bunbury mixer, a pressure kneader or a two-roll mill.
The flame-retardant resin composition of the invention can be molded to form a product with the desired shape by conventional molding methods such as injection molding, extrusion molding, vacuum molding, profile extrusion molding, blow molding, foam molding, injection press molding, gas injection molding and the like.
The flame-retardant resin composition of the invention can find wide application in various fields or industries, such as electrical, electronics or telecommunication, agriculture, forestry, fishery, mining, construction, foods, fibers, clothing, medical services, coal, petroleum, rubber, leather, automobiles, precision machinery, timber, furniture, printing, musical instruments, and the like. Stated more specifically, the flame-retardant resin composition of the invention can be used for business or office automation equipment, such as printers, personal computers, word processors, keyboards, PDA (personal digital assistants), telephones, facsimile machines, copying machines, ECR (electronic cash registers), desk-top electronic calculators, electronic databooks, electronic dictionaries, cards, holders and stationery; electrical household appliances and electrical equipment such as washing machines, refrigerators, cleaners, microwave ovens, lighting equipment, game machines, irons and kotatsu (low, covered table with a heat source underneath); audio-visual equipment such as TV, VTR, video cameras, radio cassette recorders, tape recorders, mini discs, CD players, speakers and liquid crystal displays; and electric or electronic parts and telecommunication equipment, such as connectors, relays, condensers, switches, printed circuit boards, coil bobbins, semiconductor sealing materials, electric wires, cables, transformers, deflecting yokes, distribution boards, and clocks and watches. Further, the flame-retardant resin composition of the invention can be widely used for the following applications: articles for automobiles, vehicles, ships, aircrafts and constructions, such as seats (e.g., padding, outer materials, etc.), belts, ceiling covering, convertible tops, arm rests, door trims, rear package trays, carpets, mats, sun visors, wheel covers, mattress covers, air bags, insulation materials, hangers, hand straps, electric wire coating materials, electrical insulating materials, paints, coating materials, overlaying materials, floor materials, corner walls, deck panels, covers, plywoods, ceiling boards, partition plates, side walls, carpets, wall papers, wall covering materials, exterior decorating materials, interior decorating materials, roofing materials, sound insulating panels, thermal insulation panels and window materials; and living necessities and sporting goods such as clothing, curtains, sheets, plywoods, laminated fiber boards, carpets, entrance mats, seats, buckets, hoses, containers, glasses, bags, cases, goggles, skies, rackets, tents and musical instruments.
The present invention will be described below in more detail with reference to Synthesis Examples, Examples, Comparative Examples and Test Examples. In the following description, the parts and percentages are all by weight, unless otherwise specified.